With the development of society and economy, people's demand for robots is increasing day by day. However, since artificial intelligence has not been developed to sustain independent operation, robots at present need manual intervention or pre-program to perform fixed tasks. Under such context, exoskeleton robot with perfect human-machine interaction has drawn more and more attentions from researchers. Moreover, exoskeleton robots are endowed with powerful functions. For instance, it can facilitate limb injuries to receive rehabilitation therapy, for which exoskeleton can be fastened with injured limbs to control and drive limb movement. In addition, it can help the disabled with mobility problems to recover their exercise capacity, for which exoskeleton can be used to assist the disabled limbs, for lower limb injuries to walk again or upper limb injuries to pick up items again. As for a healthy person, exoskeleton can greatly improve everyone's exercise capacity, rendering ordinary person to lift objects of hundreds of pounds without efforts, or complete a long journey of tens of kilometers. Therefore, exoskeleton with extraordinary ability has a great potential for development in military, scientific research, industrial production and daily life, which is of great positive significance to promote socio-economic development.
There are several existing control methods for exoskeleton robots. For instance, direct manual control can be used for direct control of exoskeleton robots by pressing the operating buttons, which is difficult to ensure the coordination; pre-programmed control can be used where exoskeleton robots can only exercise based on the pre-set tracks with low degree of freedom; in addition, master-slave control can be used where exoskeleton robots can be divided into master exoskeleton fixed with human limbs and slave exoskeleton driven by external force. When the master exoskeleton is driven into motion by human body, there will be a differential motion between master and slave exoskeletons, for which the angular deviation signal between them can be generally detected by an angle sensor as the driving signal of slave exoskeleton. Despite of higher degree of freedom and better coordination as compared with the aforesaid methods, such control method, with higher requirements for relatively complicated driving structures and high-precision angle sensors, requires an angular difference between master and slave exoskeletons to generate the required driving force. Therefore, there could be a lag in exoskeleton motion, which will be particularly obvious when precision of angle sensors remains low.